The present invention relates to fastener insertion apparatus and a feeder assembly therefor.
The term “fastener” is used herein to include rivets, screws, slugs and other types of fastening devices.
In one known type of fastening technology rivets are delivered to a rivet setting tool via a delivery tube in which the rivet is propelled by, for example, compressed air. At the end of the delivery tube the rivet is typically transferred to a rivet delivery passage in a nose of a setting tool. An alignment or retaining device disposed in the nose holds the rivet in coaxial alignment with the passage ready for insertion into a workpiece. When the rivet is in this position a punch descends along the rivet delivery passage and drives the rivet into the workpiece so that it is deformed by an upsetting die disposed below the workpiece. In an alternative design the fasteners are retained in a carrier tape and are advanced with the tape so that they are brought sequentially into alignment with the punch and die assembly by a feeder before the punch is actuated to drive the fastener out of the tape and into the workpiece as before.
In another current fastening method known as clinching workpieces are mechanically interlocked by deforming them into each other with or without using a fastener such as a rivet. A punch descends along a passage and impacts directly on to a workpiece so that the latter is deformed in a die disposed below the workpiece. This technology is usually used to join two or more sheets of material but can be used to form a deformation in a single sheet for locating a component to be connected to or positioned adjacent to the sheet.
Modern mechanical joining tools such as, for example, rivet setters are generally microprocessor controlled and often combined with robot technology. The tools are operated under the control of a computer program that provides instructions relating to the joining position and type (including fastener type (if any) and process parameters) for each joint to be effected in a particular workpiece. The type of fastening to be used is selected according to many factors including the size of the parts to be connected. A fastener delivery system associated with the tool must thus be able to cope with the supply of rivets of different sizes and types in any particular sequence without increase to the fastening cycle time and the tool must be able to produce a clinched joint with or without a fastener.
Fasteners having different aspect ratios (fastener length to head diameter) are fed in different orientations. For example, fasteners with a low aspect ratio are susceptible to tumbling in the delivery tube, which must therefore be of T-shape, or rectangular cross-section and fasteners with a high aspect ratio are typically transported axially in tubes of circular cross-section
In certain fastening applications several rivet sizes are required for a workpiece or section of a workpiece if, for example, it comprises overlapping sheets or there is a requirement to attach a bracket to another component, in which case the sandwich thickness of the workpiece varies from two sheets to three sheets or more. In other applications it may be necessary to have a mix of riveted and clinched joints. When self-piercing riveting technology is employed, one of the factors determining the strength of a riveted joint is the length of the rivet in relationship to the sandwich thickness of the material to be fastened. When clinching technology is employed, the geometry and size of both the punch and the die and the presence or absence of an additional fastener are important factors in the performance of the joint. The mechanical properties of joints riveted with the same size of rivet will vary depending on the sandwich thickness and the material being fastened. In a continuous production environment, conventional self-piercing riveting tools are generally dedicated to a single rivet size and the problem of riveting combinations of different thicknesses and types of material that cannot be accommodated by a single rivet size is addressed by using several dedicated tools each applying a different rivet size. Obviously this requires careful planning as increased combinations of different joint thicknesses, types and strengths require additional rivet sizes and/or different clinching processes and therefore increased numbers of tools. Certain known fastening tools have twin feeds and are able to supply more than one type of fastener but they generally cannot supply a large range of fasteners and the feeding of fasteners to the nose of the tool can be unreliable. It would clearly be desirable to provide reliable fastener insertion apparatus capable of delivering a large range of fastener sizes as this would enable production environments to rationalize tool costs including economizing on spare parts and back-up systems.
In applications of this kind rivet delivery can be a problem in that there is no provision for dealing with a plurality of rivets that may have been accidentally fed into the nose. Moreover, effective delivery relies purely on the momentum of the rivet as it travels down the delivery tube. It will be understood that the rivet momentum is variable with the air pressure supply (that propels the rivets along the tube), rivet mass and restrictions in the passage of the delivery tube (caused by kinks, bends, dirt and wear etc).
Finally, there is generally a slow cycle time associated with such transfer arrangements. Rivets are fed separately to the nose and the cycle time is thus dependent on the length of the delivery tube.
In a known configuration a transfer station is disposed between the nose and the delivery tube. Rivets are stopped at the transfer station and are transferred to the nose by a pusher. While this arrangement reduces the cycle time in that rivets can be collected at the transfer station, the other disadvantages referred to above are not solved.
Our European Patent No. 0746431 describes a fastening machine in which rivets are supplied under pressure via a delivery tube to the rivet delivery passage in the nose of a setting tool. The delivery tube may be T-shaped rectangular or of other profiled section. The rivet enters the delivery passage in a substantially perpendicular direction and is supported therein by balls, rollers or other protrusions prior to engagement of the punch with the rivet. A limit switch is used to sense the presence of a rivet in the delivery tube and issues a signal to a controller to indicate that the punch may be actuated. The travel of the rivet through the delivery passage under the punch is controlled by a vertical array guide elements such as rows of balls or fingers or other protrusions on the wall of the delivery passage.
Our European Patent application No. 99936862.4 describes many aspects of a fastener delivery system. One aspect is concerned with the transfer of fasteners from the delivery tube or magazine into the fastener delivery passage of a nose of the setting tool. In all embodiments there is a transfer station that manages the transfer of the fasteners individually into the nose while ensuring that they are correctly aligned with the punch. In all embodiments the fastener is delivered under pressure in a tube to a gate at the transfer station where its presence is sensed and a pusher is used to force the fastener through the gate into the nose. The pusher is then retracted prior to advance of the punch so as to prevent damage to the transfer station. Once the rivet has been passed from the transfer station into the nose there is no means for checking it has been safely loaded.
European patent application No. 0922538 (Emhart) describes a feeder arrangement for transferring fasteners into a fastener delivery passage of a setting tool. The arrangement comprises a fastener feed duct having a T-shaped cross-section in which fasteners are delivered to a transfer station immediately adjacent to the nose of the setting tool. The transfer station comprises a conveying duct with a catch unit in the roof thereof. When the fastener is supplied its head comes into frictional contact with the catch and is decelerated slightly before it passes into the nose so as to ensure reliable passage of the fastener into the nose. The catch can prevent a head of a rivet from falling back through an entry port in the nose but it does not prevent a long-stemmed rivet from swinging back into the supply passage.
It is an object of the present invention to provide for an improved fastening apparatus that operates with increased reliability, accommodates fasteners of differing lengths and can selectively effect joining by fastener insertion or clinching.